This invention relates to a hydrogen storage alloy electrode, particularly to an active material of hydrogen storage alloy electrode.
A good many of researches have been taken on selecting the active material which may be used for preparing the hydrogen storage alloy electrode during the past twenty and more years. The LaNi.sub.5 alloy was chosen initially but the life of the alkali batteries assembled with the electrodes prepared from the LaNi.sub.5 alloy was too short. To improve the alkali batteries, many compositions were given, such as Iwakura, C disclosed in Journal of the less-Common Metal 159, 127 (1990), who substituted Co for part of Ni in the LaNi.sub.5 to prepare LaNi.sub.5 - xCox ternary alloy. The recent representative improvement is the alloy with composition of MmNi.sub.3.8 Co.sub.0.5 Mn.sub.0.3 Al.sub.0.3 as described in JP63-175339 and JP63-264869 (1988). However, the cycle lives of alkali batteries assembled with the electrodes prepared from the alloys of aforementioned LaNi.sub.5 system of titanium system, zirconium system and calcium system are still not ideal up to now.
It has been found by analysis that the cause lies not only in the stability of the active material itself of the hydrogen storage alloy anode, but also concerned with the nickel oxide cathode of this kind of alkali battery suffered with the corrosion from the electrolyte during the charge - discharge process and the corrosive reaction may be aggravated in pace with the increase of charge-discharge times. The measure adopted generally is to add LiOH at a specific ratio into the KOH electrolyte before sealing of the battery as to protect the nickel oxide cathode. Nevertheless, the effect of this protective measure is not satisfactory. If the LiOH concentration of the electrolyte may be raised along with the cycles of charge-discharge process, the effect of the cathode protection should be improved apparently and the cycle life of the battery should be prolonged greatly. However, it is impossible to add LiOH in the charge-discharge process after sealing up of the battery.